overleaf/services/web/public/js/libs/polyfills/array-includes.js

define([], function() {
  // https://tc39.github.io/ecma262/#sec-array.prototype.includes
  if (!Array.prototype.includes) {
    Object.defineProperty(Array.prototype, 'includes', {
      value: function (searchElement, fromIndex) {

        if (this == null) {
          throw new TypeError('"this" is null or not defined');
        }

        // 1. Let O be ? ToObject(this value).
        var o = Object(this);

        // 2. Let len be ? ToLength(? Get(O, "length")).
        var len = o.length >>> 0;

        // 3. If len is 0, return false.
        if (len === 0) {
          return false;
        }

        // 4. Let n be ? ToInteger(fromIndex).
        //    (If fromIndex is undefined, this step produces the value 0.)
        var n = fromIndex | 0;

        // 5. If n ≥ 0, then
        //  a. Let k be n.
        // 6. Else n < 0,
        //  a. Let k be len + n.
        //  b. If k < 0, let k be 0.
        var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

        function sameValueZero(x, y) {
          return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
        }

        // 7. Repeat, while k < len
        while (k < len) {
          // a. Let elementK be the result of ? Get(O, ! ToString(k)).
          // b. If SameValueZero(searchElement, elementK) is true, return true.
          if (sameValueZero(o[k], searchElement)) {
            return true;
          }
          // c. Increase k by 1.
          k++;
        }

        // 8. Return false
        return false;
      }
    });
  }
})